In sewing machines that can perform buttonhole sewing, it is necessary to change the sewing length of a buttonhole according to the diameter of a button. For example, computer sewing machines disclosed in JP 2010-227391A (Reference 1), JP 8-141235A (Reference 2), and JP 2008-12052A (Reference 3) have a detection mechanism that detects the diameter of a button, and are adapted to be able to automatically move cloth that becomes an object to be sewn according to the detected diameter of the button in a front-and-rear direction, and to automatically sew a buttonhole with a predetermined length according to the diameter of the button.
The computer sewing machine disclosed in Reference 1 includes a buttonhole switch mechanism constituted by a buttonhole presser mounted on a lower end of a presser bar of the sewing machine, a buttonhole switching arm attached so as to be rotatable in a feed direction with a rotary shaft anchored to an upper left end of a machine frame of the sewing machine as a supporting point, a buttonhole switching lever attached so as to be movable vertically with respect to the buttonhole switching arm, and a detection switch fixed to an upper left end of the machine frame and having contacts electrically connected by the rotation of the buttonhole switching arm. When the buttonhole sewing is performed, first, a button is mounted on the buttonhole presser, and the interval of two projection portions formed on the buttonhole presser is adjusted to an interval according to the diameter of the button. Next, the buttonhole switching lever is pulled down to between the two projection portions. Then, if the buttonhole sewing is started, as the buttonhole switching lever abuts against each projection portion, the buttonhole switching arm is rotated, and the detection switch is electrically connected. Thereby, the cloth that becomes an object to be sewn moves automatically in the front-and-rear direction.
In addition, the invention disclosed in Reference 1 relates to a sewing machine that suppresses occurrence of stitch skipping in a stepped portion during double fabric sewing, and a structure in which a movable portion of a double fabric sewing presser mounted on a lower end of a presser bar is combined with the above buttonhole switching lever is described in Reference 1. According to this structure, the buttonhole switching lever is rotated and the detection switch is electrically connected in conjunction with the vertical movement of the movable portion of the double fabric sewing presser during double fabric sewing (step ascent, step descent). Then, by operating a needle and shuttle timing adjustment mechanism in conjunction with the electrical connection of the detection switch, it is possible to adjust the encounter timing between the sewing needle and the shuttle to prevent occurrence of stitch skipping of a seam.
In the computer sewing machine disclosed in Reference 2, a housing of a sewing machine main body is equipped with a BH sensor that detects the diameter of a button. The BH sensor is constituted by a detection lever, a button case, and a sliding volume (variable resistor). If the detection lever is moved and a button is inserted between the inner wall of the button case and the detection lever after the button is set in the button case, the resistance value of the sliding volume can change according to the travel distance of the detection lever, and the diameter of the button corresponding to the resistance value can be detected. Then, in CPU of the sewing machine, sewing data of the buttonhole is created on the basis of the detected diameter of the button and a cloth feed amount set by a user, and the buttonhole sewing is automatically performed on the basis of this sewing data.
The computer sewing machine disclosed in Reference 3 has a sliding volume built into a buttonhole presser mounted on a lower end of a presser bar of the sewing machine. The buttonhole presser is equipped with a presser body fixed to the presser bar, and a presser frame that slides in a front-and-rear direction with respect to the presser body, and the amount of relative displacement between the presser body and the presser frame can be detected by the sliding volume. In this sewing machine, the buttonhole sewing is automatically performed while performing detection of the diameter of a button mounted on the buttonhole presser depending on a change in the resistance value of the sliding volume and performing regular detection of the position of the buttonhole presser.
In the sewing machine disclosed in Reference 1, in order to ensure the quality (appearance) of the buttonhole sewing, it is necessary to electrically connect contacts of the detection switch precisely according to a predetermined amount of rotation of the buttonhole switching arm. For this reason, in a sewing machine manufacturing process, an adjustment mechanism and an adjustment process with which a manufacturer (worker) is able to adjust the electrical connection position of the detection switch are required. Although the adjustment of the electrical connection position of the detection switch is not described in Reference 1, the adjustment of the electrical connection position is performed as will be described below. Side views schematically illustrating the buttonhole switch mechanism of the sewing machine described in Reference 1 are shown in FIGS. 11A to 11C. In FIG. 11A, 7 represents a buttonhole presser, 120 represents a lever member in which a buttonhole switching arm and a buttonhole switching lever are integrally expressed, 23 represents a detection switch, and 124 represents a mount of the detection switch 23. A rotary shaft 120c of the lever member 120 and a rotary shaft 124a of the mount 124 are fixed to a non-movable part of a sewing machine main body, respectively. As shown in FIG. 11B, the detection switch 23 is a two-contact-type switch that has a central contact 23a, a rear contact 23b, and a front contact 23c. 
Before the adjustment of the electrical connection position of the detection switch 23, as shown in FIG. 11B, the contact spacing between the central contact 23a and the rear contact 23b and the contact spacing between the central contact 23a and the front contact 23c are an equal spacing F3. In a case where a push-in amount F2 of a lower end portion 120b to the front is large when the lower end portion 120b of the lever member 120 is brought into contact with a projection portion 72a of the buttonhole presser 7 as shown in FIG. 11A in order to start the buttonhole sewing, the travel distance of the central contact 23a to the rear, which is moved by a switching operation portion 120a of an upper end of the lever member 120 also becomes large. At this time, in a case where the central contact 23a is brought into a state where the central contact is excessively pushed into the rear contact 23b side, the quality of the buttonhole sewing is impaired due to the shift of the electrical connection position of the detection switch 23. Thus, a manufacturer rotates the mount 124 around the rotary shaft 124a to adjust the contact spacing between the central contact 23a and the rear contact 23b of the detection switch 23 to F5 larger than F3 (shown in FIG. 11C). Thereby, it is possible to avoid the central contact 23a being excessively pushed into the rear contact 23b side at the time of the start of the buttonhole sewing.
There are problems to be described below in the adjustment mechanism for the electrical connection position of the above-described detection switch 23. First, in the above-described adjustment mechanism, adjustment is performed by manufacturer's trial and error. Therefore, in a case where the number of times of repetition of trial and error increases, there is a problem in that work man-hours may increase and manufacturing costs may rise. Secondly, in the above-described adjustment mechanism, adjustment is performed by a skilled manufacturer, and it is difficult for a user to perform adjustment. For this reason, in a case where a defect occurs again in the electrical connection position of the detection switch 23 after use of the sewing machine, there is an inconvenience that a user needs to make a request to a maker or the like to repair the sewing machine.
Thirdly, the contact spacing between the central contact 23a and the front contact 23c is reduced from F3 to F4 by increasing the contact spacing between the central contact 23a and the rear contact 23b from F3 to F5 (shown in FIG. 11C). At this time, in a case where the amount of adjustment of the electrical connection position of the detection switch 23 is large and the contact spacing F4 becomes excessively small, the shift gap of the timing at which the direction in which cloth is fed is reversed becomes marked. That is, in a case where the contact spacing F4 is small when the lower end portion 120b of the lever member 120 contacts a projection portion 71a of the buttonhole presser 7 and the direction in which the cloth is fed is reversed, the direction in which the cloth is fed is reversed at an early timing. Thereby, there is a problem in that the sewing length of a buttonhole becomes shorter than a setting value. Fourthly, in the above-described adjustment mechanism, the rotary shaft 120c of the lever member 120 is fixed to the non-movable part of the sewing machine main body. Therefore, in order to keep the push-in amount F2 of the lever member 120 within an adjustable range of the electrical connection position of the detection switch 23, there are problems in that excessively high dimensional precision of sewing machine component parts and excessively high assembling precision of a sewing machine manufacturing process are required and manufacturing costs rise.
Side views schematically illustrating a buttonhole switch mechanism different from the buttonhole switch mechanism of the sewing machine described in Reference 1 are shown in FIGS. 12A to 12C. Although the buttonhole switch mechanism shown in FIGS. 12A to 12C has the structure in which the detection switch 23 and the lever member for operating the detection switch 23 are combined similarly to Reference 1, the buttonhole switch mechanism includes an adjustment mechanism for the electrical connection position of the detection switch 23 that is different from Reference 1. As shown in FIG. 12A, a lever member 220 of the buttonhole switch mechanism is split into a lever body 221 and an adjusting portion 222, and is adapted to be able to change an angle H1 formed between the lever body 221 and the adjusting portion 222. The lever member 220 in which the lever body 221 and the adjusting portion 222 are integrated is rotatably supported by a rotary shaft 220c fixed to the non-movable part of the sewing machine main body.
As shown in FIG. 12B, before the adjustment of the electrical connection position of the detection switch 23, the angle H1 formed between the lever body 221 and the adjusting portion 222 is 180°. In the sewing machine manufacturing process, when a manufacturer brings a lower end portion 220b of the adjusting portion 222 into contact with the projection portion 72a of the buttonhole presser 7, a state, where a push-in amount H2 of the lower end portion 220b to the front is large and the contact of the detection switch 23 is excessively pushed in by a switching operation portion 220a of the upper end of the lever body 221, is brought about. At this time, as shown in FIG. 12C, the excessive push-in amount of the contact of the detection switch 23 can be reduced as a manufacturer changes the angle H1 formed between the lever body 221 and the adjusting portion 222 to an angle smaller than 180°.
There are problems to be described below in the adjustment mechanism for the electrical connection position of this detection switch 23. First, the inclination of the adjusting portion 222 becomes large as the amount of adjustment of the angle H1 increases. Thereby, the effective width (horizontal distance between a contact of the lower end portion 220b with the projection portion 71a and a contact of the lower end portion 220b with the projection portion 72a) of the lower end portion 220b of the adjusting portion 222 increases from an effective width H3 shown in FIG. 12B to an effective width H4 shown in FIG. 12C. Also, as the effective width of the lower end portion 220b increases, the direction in which the cloth is fed is reversed at an early timing. Thereby, there is a problem in that the sewing length of a buttonhole becomes shorter than a setting value. Secondly, the rotary shaft 220c of the lever member is fixed to the non-movable part of the sewing machine main body. Therefore, in order to keep the push-in amount H2 of the lower end portion 220b of the adjusting portion 222 within an adjustable range of the electrical connection position of the detection switch 23, there are problems in that excessively high dimensional precision of the sewing machine component parts and excessively high assembling precision of the sewing machine manufacturing process are required and manufacturing costs rise.
In the sewing machine disclosed in Reference 2, the sliding volume is used for the detection mechanism that detects the diameter of a button, and in the sewing machine disclosed in Reference 3, the sliding volume is used for the detection mechanism for the diameter of a button and the position of buttonhole presser. In the sewing machines disclosed in References 2 and 3, the adjustment mechanism for the electrical connection position of the detection switch 23 in the above-described Reference 1 becomes unnecessary due to using the sliding volume. Accordingly, in the sewing machines disclosed in References 2 and 3, the above-described problems, that is, the problem that the sewing length of the buttonhole becomes shorter than a setting value, the problem that excessively high dimensional precision of the sewing machine component parts is required, and the problem that excessively high assembling precision of the sewing machine manufacturing process is required are solved.
Incidentally, since the sliding volume is used in the sewing machines disclosed in References 2 and 3, there are problems to be described below. First, since the sliding volume is expensive as compared to the buttonhole switch mechanism described in Reference 1 in which the detection switch and the lever member for operating the detection switch are combined, there is a problem in that product costs rise. Secondly, in the sliding volume, variation or hysteresis of resistance value occurs even within the same manufacturing lot. Therefore, the sewing machine manufacturing process requires an adjustment mechanism and an adjustment process such that a manufacturer electrically changes the resistance value of the sliding volume or changes the setting value of a calibration factor by which the resistance value of the sliding volume is multiplied using software. In this adjustment process, adjustment is performed by the manufacturer's trial and error. Therefore, in a case where the number of times of repetition of the trial and error increases, there is a problem in that work man-hours may increases and manufacturing costs may rise.
Moreover, in the sewing machine disclosed in Reference 3, the sliding volume is built into the buttonhole presser. Therefore, it is necessary to connect a harness extending from the buttonhole presser to a connecting portion of the sewing machine main body. Accordingly, there is inconvenience that a user should pay attention so that the cloth is not entangled in the harness when the cloth that becomes as an object to be sewn is set in the sewing machine or during sewing.
This disclosure has been made in view of the above-described circumstances, and a need thus exists for a buttonhole switch mechanism of a buttonhole sewing machine in which product costs are inexpensive by using a buttonhole switch mechanism in which a detection switch and a lever member for operating the detection switch are combined and in which excessively high dimensional precision of sewing machine component parts and excessively high assembling precision of a sewing machine manufacturing process are not required by including an adjustment mechanism that can easily adjust the electrical connection position of the detection switch.